Spin thermal conductivity of the Haldane chain compound Y2BaNiO5

We report experimental results on the thermal conductivity of the spin S=1 chain compound Y2BaNiO5 in the temperature range between 5.5 and 300K. The results show a clear anisotropic behavior of the thermal conductivity along different lattice directions. The contributions to the total thermal conductivity provided by phonons and magnons are estimated. The spin-related energy diffusion constant DE(T), calculated from the experimental data of the magnon thermal conductivity, is approaching the theoretically predicted high-temperature limiting value close to room temperature. With decreasing temperature, DE(T) increases reaching a broad peak at about 120K. At low temperatures, the scattering of spin excitations by magnetic impurities seems to be the major factor limiting the magnon thermal transport